Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

573
FXUS63 KLOT 091937
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
237 PM CDT Thu Jul 9 2026

.KEY MESSAGES...

- A threat for isolated to widely scattered thunderstorms
  through this evening.

- Mainly dry and increasingly warm weather this weekend onward,
  though it will be cooler lakeside until later next week.

&&

.DISCUSSION...
Issued at 237 PM CDT Thu Jul 9 2026

This Afternoon:

A weak remnant MCV (mesoscale convective vortex) has slowly
pushed across the area through early this afternoon. It appears
that the timing of the disturbance was early enough to curtail
stronger destabilization from a combination of thicker cloud
cover and already marginal mid-level lapse rates of <6C/km.
Forcing on the backside of the MCV, subtle confluence, and a bit
better destabilization south of I-80 recently enabled an uptick
in coverage of smaller footprint pulse type convection. As the
forcing from the MCV pushes farther east, a somewhat subsident
regime may result in the current activity struggling for a bit.
Farther north, the aforementioned more subsident regime as well
as meager low-level convergence from close to due westerly
boundary winds will probably keep convective coverage at a
minimum for a few hours.

Late Today through Tonight:

Based on upstream radar presentation as of this writing, a weak
approaching cold front should provide enough lift for a modest
uptick in showers and isolated to widely scattered thunderstorms.
Winds shifting onshore near the lake from an early evening lake
breeze could plausibly provide modestly a modestly enhanced
focus. However, the weakly forced, weak deep layer shear, and
modest mid-level lapse rate environment does not appear that it
will be conducive to much in the way of storm organization.
Earlier concerns of localized flash flooding appear to be
trending downward even if a few storms materialize into this
evening, as they will likely continue to be smaller footprint
and pulse-type (shorter-lived). Favorable moisture parameters
and high freezing levels would thus be offset by limited areal
coverage and duration of any heavy rainfall. If a more focused
corridor of showers and embedded storms does not materialize by
this evening, with a likely diurnal component to the activity,
the flood threat for the rest of the night should be limited.

Overnight into early Friday as the cold front sags south, light
winds and low dew point spreads may support fog development and
localized visibility below 1 mile. Maintained areas of fog
mention closer to the lake in northeast Illinois and far
northwest Indiana, though confidence isn`t all that high.

Friday Onward:

The sagging front will force the instability axis southward
Friday and Saturday, and with it the threat for any showers and
storms. Have confined chance PoPs to near and south of the
Kankakee River Friday afternoon and evening and then primarily
south of US-24 on Saturday afternoon (which may be too generous).
For the rest of the area, a couple pleasant days with more
comfortable humidity levels, and seasonably warm temperatures
in the lower to mid 80s are in store. Synoptic onshore flow from
surface high pressure settling over the Great Lakes will keep
highs near the lake in the mid 70s to around 80F.

For Sunday into early to mid next workweek, an expansive and
anomalously strong/warm mid-level ridge will establish itself
from the central and northern Plains to the Midwest.
Increasingly warm 850 to 925 mb temps underneath the influence
of the ridge will result in a warming trend away from the lake.
Meanwhile, the surface high pressure will remain in place until
midweek or thereabouts, resulting in daily lake breezes and
associated lake cooling. In addition, dew points and thus
humidity levels will be held in check vs. our previous very warm
to hot stretch. The ridge may become sufficiently flattened
sometime later next week for a return of convective chances.
Until then, a several day stretch of continued drying will help
river and streams to return back to more typical flows.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1241 PM CDT Thu Jul 9 2026

Aviation forecast concerns for the 18Z TAFs:

- Scattered convective SHRA/isolated TSRA likely across
  terminals especially late afternoon into early/mid evening.
  IFR/low-MVFR vis possible in brief heavy rain.

- MVFR ceilings develop late tonight with a period of IFR
  possible toward daybreak. Fog also possible from Chicago Lake
  Michigan shore west/northwest with MVFR/IFR vis possible.
  Improvement to VFR expected around midday Friday.

- Weak cold frontal passage this evening will shift winds to the
  N/NE. NE winds persist through Friday.

A weak mid-level circulation (remnant MCV from overnight
convection to our west) was tracking east across northern IL at
midday, atop a moist low-level air mass ahead of a weak, slowly-
approaching cold front. Scattered showers have been percolating
near and ahead of the weak MCV, though extensive cloud cover and
weak lapse rates have limited the depth of this convection and
no lightning has been observed near the terminals at this time.
Shower and eventually isolated thunderstorm coverage is
expected to increase somewhat during the mid-late afternoon
hours however, as a low-amplitude mid-level wave and the weak
cold front approach during our peak diurnal warmth. Thus the
greatest TSRA potential for the terminals looks to be from late
this afternoon into early this evening, though coverage will
likely remain only widely scattered. Have trimmed TS mention to
VC/PROB30 based on these expectations.

Scattered SHRA may persist into the overnight hours, as the weak
cold front eventually moves slowly through the area. Modest
west-southwest winds are expected to turn north-northeasterly
behind the front overnight, and remain north-northeast through
the day Friday. High-res guidance continues to support fairly
extensive MVFR ceilings after midnight behind the front, which
may linger as late as midday Friday. Guidance also indicates the
potential for a period of IFR ceilings and MVFR/IFR fog from
the IL Lake Michigan shore north and west during the predawn
hours, and have included a tempo mention for this. While
visibility should improve a few hours after sunrise, ceiling
improvement to VFR may not occur until midday.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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